Peat is commonly used as a filtering medium, both in its raw state as well as in a form which has been chemically treated from its parent material; yet, its application is severely limited by certain inherent characteristics of the material itself. For example, raw peat is physically quite restrictive to the flow of liquid or effluent to be filtered. In addition, it contains fulvic acid which as a soluble fraction can contribute to soluble organic contamination and thus increase the biological oxygen demand; also this soluble organic fraction has been shown to react with chlorine to produce chlorinated organic carcinogens.
Many forms of chemically modified peat have been developed and proposed for use as water filtering media. Activation of peat, either by air-oxidation or wet-oxidation methods, results in the formation of a medium similar to certain activated charcoals that are capable of removing hydrophobic compounds from aqueous solutions. Unlike the activated charcoals, the chemically modified peats have the capacity to remove heavy metal cations from the filtrant. Nonetheless, these peat materials have several limitations in terms of preparation costs, their tendency to chip and shed; and more importantly, have serious chemical limitations, such as, swelling and leaching of organic matter in the presence of alkaline or detergenated solutions.
Synthetic ion-exchange resins which incorporate an inert matrix material, such as, polystyrene or other plastics include an active agent which can exchange a cation for a less desirable cation, or an anion for another anion. These resins, however, are so costly to manufacture that they are generally much too expensive to be used in industrial or commercial applications on a large scale basis. All ion-exchange resins, while useful for cation and anion exchange, have no significant capability for removal of hydrophobic compounds.
U.S. Pat. No. 4,459,149 to E. F. Moran et al is directed to a process for treating humus material including peat which in an intermediate stage of its process forms a dry filter cake which is then converted to a humate salt or to a humic acid; the patent is essentially concerned with the formation of humic substances for agricultural purposes but not to the formation of a filtering medium as an end product. U.S. Pat. No. 3,328,158 to A. L. Marks is directed to the preparation of organic fertilizer by combining nutrient materials with a readily soluble humic acid, such as, peat and of solubulizing materials by a pressurized cooking process followed by the addition of selected calcium-magnesium materials together with nitric acid and phosphoric acid. Other representative patents are U.S. Pat. No. 2,093,047 to J. Wageningen et al; U.S. Pat. No. 2,158,918 to C. S. Townsend et al; U.S. Pat. No. 2,317,990 to E. F. Grether; U.S. Pat. No. 2,992,093 to E. M. Burdick; U.S. Pat. No. 3,321,296 to R. Abbe; U.S. Pat. No. 3,398,186 to N. N. Schwartz; U.S. Pat. No. 3,603,643 to M. Hirota et al; U.S. Pat. No. 3,617,237 to S. Nagasawa et al; U.S. Pat. No. 3,674,649 to M. Formisano et al; U.S. Pat. No. 3,770,411 to J. C. Chambers et al; and U.S. Pat. No. 4,223,449 to W. Bodle et al.
It is proposed in accordance with the present invention to provide for a novel and improved multi-purpose filtering medium which is specifically adapted to use in water and possibly air filtration in which a peat source is chemically modified in such a way as to greatly enhance its filtering capabilitiies. More specifically, a method of producing a filtering medium from a peat source is proposed which is economical, suitable for high volume production, and capable of producing a material which is stable with high ionic exchange rates and hydrophobic absorption over a wide pH range.